Your type of analysis is generally the correct one used in legal thought. If the MLB's burden was less than the probability of harm times the degree of loss, then they should be held liable for damages. B < p x L However, this all goes out the window when there is an express assumption of risk involved, as there is with participating in professional sports. Thus, fear of liability is a moot point, unless it is somehow considered to be gross negligence and/or outside the scope of the assumption of risk. For example, several fans were hurt a few years ago at Coors Field when the escalator had a brain fart and threw everyone down. An escalator collapse is outside the scope of one's "assumption of risk", getting hit by a foul ball or a stray puck isn't. Thus, the Rockies were held liable. If MLB wants to put helmets on their base coaches, it's unlikely they would be doing it for legal reasons, otherwise they'd be putting helmets on umpires, pitchers, fielders, guys in the dugout, etc.